A pure substance has no degrees of freedom at one of these, according to a rule named for Gibbs, and any system has p choose 
A pure substance has no degrees of freedom at one of these, according to a rule named for Gibbs, and any system has p choose 3 of these, where p is the number of [*] phases. Helium-4 has two unconventional ones due to superfluidity, while for water, it fixes the definition of the Kelvin scale and is at .612 kilopascals and 273.15 Kelvins. For 10 points, name this point where coexistence curves meet on the phase diagram, a temperature and pressure at which a substance exists in an equilibrium of all three phases of solid, liquid, and gas.
A pure substance has no degrees of freedom at one of these, according to a rule named for Gibbs, and any system has p choose 3 of these, where p is the number of [*] phases.
{triple} point